When making large wind turbine blades it has become practice to use semi-finished components with fibres in a layer of resin, i.e. a composite material. These semi-finished components can be called pre-forms. The components can, depending on their structure, provide strength primarily in one direction and they can therefore be used as reinforcement elements for the wind turbine blades.
Traditionally, “endless” sheets of a single layer of fibres in a resin have been manufactured as piece-goods. Subsequently, the sheets have been cut into smaller parts having the required shape and size. These parts have been stacked and laminated to achieve a finished reinforcement element; i.e. a pre-form.
Therefore, the traditional method causes generation of waste products as it is impossible to use the entire sheet when cutting it into smaller parts of required shape and size. As the sheets are expensive, the traditional method creates a high loss of value due to the size of the waste product. Furthermore, the cutting is time consuming and therefore increases the manufacturing costs.
In the traditional method, the sheets are cut after the fibres have been wetted in resin and this sometimes causes problems when resin adheres to the cutting device. This again increases the demand for specially designed cutting tools for cutting the wet and thus tacky sheets. Often, the pre-wetted sheets of fibres are referred to as pre-pregs. In the traditional manner where pre-pregs are cut into the desired shape, the problem with waste material increases further since the waste material contains uncured and potentially harmful resin.
When stacking the pre-pregs, air can be trapped between the layers. As the layers are semi-finished components with fibres in a layer of resin it can be difficult to remove the air being trapped between the layers.